Info

/Macropiper

/Piper

/Ottonia

/Enckea

/Schilleria

/Radula

/Pothomorphe

/Macropiper

/Piper

/Ottonia

/Enckea

/Schilleria

/Radula

/Pothomorphe

/Macrostachys

/Macrostachys

Inflorescence Types

Inflorescence Types

FIGURE 10.4. Evolutionary history of flowers and inflorescences in the genus Piper. Simplified phylogeny from Fig. 10.2. In each floral diagram, circles are stamens, triangles and squares are ovaries, arching lines are floral bracts.

FIGURE 10.4. Evolutionary history of flowers and inflorescences in the genus Piper. Simplified phylogeny from Fig. 10.2. In each floral diagram, circles are stamens, triangles and squares are ovaries, arching lines are floral bracts.

only the first pair of stamens originates (Tucker et al. 1993). However, this explanation does not seem to be universal. The evolution of single staminate flowers occurred both in the American and Asian tropics. The single staminate flowers of P. khorthalsii (Philippines) and P. kegelii (Amazon Basin) cannot be explained by packaging of the inflorescences since, in both species, flowers are loosely arranged in the inflorescences. Some clues to understanding the evolution of these unique flowers may be found by studying their flower development and reproductive biology.

Besides differences in reproductive system (dioecy vs. hermaphroditism) and stamen number, other categories of variation can be found in Piper flowers. Some of this variation is exhibited in the relative size of anthers and filaments, the orientation of the anther dehiscence, and the length of the style and stigma lobes. However, it is difficult to talk about the patterns of evolution of these characters; they are usually used as differentiating characters and are not useful to group and classify taxa. More studies of structure development as well as investigations linking morphologies with function may shed light on other flower-related evolutionary trends in the genus.

10.4.2. Plant Architecture

In addition to flower variability, most variation among Piper taxa is in their architecture. Piper species occur as shrubs of different sizes (50 cm to 6 m) and shapes (highly ramified or single-stemmed) and as lianas; despite these differences, Piper species are very homogeneous in their construction. Their architecture can be characterized by Petit's model (Halle et al. 1978), which consists of a monopodial, orthotropic trunk that grows continuously, and gives rise to lateral, plagiotropic, sympodial branches (Fig. 10.5). In Piper, the branches are composed of monophylls, modules constituted by an internode, an inflorescence, a prophyll, and a leaf (Blanc and Andraos 1983). Differences in appearance result from modifications of the ramification pattern and are related to the light environment in which the plant grows and the clade affiliation. An upright appearance, characteristic of the /Radula and /Macrostachys clade, has an unbranched main axis with lateral branches that ramify occasionally (Fig. 10.5). A more rounded appearance is exhibited by taxa of /Ottonia, /Schilleria, and /Enckea, where the main axis branches and has reiterations along its whole length, and the lateral branches are often ramified (Fig. 10.5). Species that have an upright look are found mostly in forest gaps and edges. Species with a ramified principal axis are favored in the understory, where the plants receive very faint light (Blanc and Andraos 1983).

A particular case of modification in the architecture as an adaptation to the environment is that of the dwarf pipers of the Choco Region (northwestern slope of the Andes). These plants were all included in Trianaeopiper Trelease, an endemic genus from the Choco ; they are very small herbs with axillary inflorescences. An initial phylogenetic analysis of the genus Piper showed that species recognized as Trianaeopiper are embedded within Piper and do not form a clade (Jaramillo and Manos 2001). Closer examination of these species showed that they are part of three (or two) distinct clades (Fig. 10.6) and the apparent axillary position of the inflorescences is a byproduct of the general reduction of axis that produced a dwarf appearance (Jaramillo and Callejas 2004). A dwarf habit is achieved by the reduction of some or all of the following architectural elements:

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